Optimization of semiconductor fabrication sometimes requires a thicker nonconducting film on some components than on other components. Such films of different thicknesses can be made by traditional mask and etch techniques or by selective deposition of the reaction product of TEOS and ozone.
Traditional mask and etch methods of forming oxide layers and spacers of different thicknesses requires the application of a first mask over select parts of the semiconductor device and then depositing a layer of silicon oxide over the unmasked parts of the semiconductor device. The first mask is then removed and a second mask is applied over the parts that have been coated with the first silicon oxide layer leaving other parts unmasked. Subsequently, a second silicon oxide layer is deposited on the unmasked parts. Finally, an etch is used to remove silicon oxide from select surfaces, leaving behind an oxide layer or spacers where desired. This process adds a number of steps to the manufacturing procedures thereby increasing the complexity of the fabrication. As such, semiconductors are typically manufactured oxide with oxide layers or spacers of an intermediate thickness that will work acceptably, although not optimally, for substrates of different conductivity or composition.
The selective deposition of TEOS/ozone on silicon in preference to silicon nitride has been disclosed in the prior art. Copending U.S. patent application Ser. No. 09/652,188 filed Aug. 31, 2000 discloses selective deposition of TEOS/ozone wherein the selectivity is based on differences in the doping of silicon. In situations where these selective deposition techniques are usable they provide means to form different thickness oxide layers in one step, thereby saving process time. The current invention improves upon the selectivity of these methods.
A hallmark of the current invention is the provision of a process that selectively deposits silicon oxide based on the characteristics of the underlying substrate and pulsed delivery of the reactants.